1. Field of the Invention
The present invention relates to a system for carrying out a connection management of a ring network which comprises a plurality of nodes connected in series via a ring line.
In the ring network, a connection management must be effectively performed for stopping the network operation when an abnormality occurs in the network and for restarting the network after the abnormality is eliminated, by determining whether the ring network is correctly formed as a ring through all of the nodes accommodated therein.
Specifically, the present invention refers to a ring network having a ring line, i.e., ring-form data transmission line. The present invention is preferably applied to a network having a single ring line, but as will be understood hereinafter, the present invention is also applicable to a ring network which, although having double ring lines, is often operated as a ring network having a single ring line. The single ring line connects a plurality of nodes, such as terminal stations, to realize a data transmission and reception thereamong. Each node is provided with at least one processor.
In general, the use of double ring lines increases the reliability of a ring network, but a single ring line is sufficient for some ring networks, such as a dispersed multiprocessor system. In such a multiprocessor system, there is little likelihood of damage to the transmission line, i.e., the ring line, compared with the probability thereof in a long distance data transmission system for intercity connections. Accordingly, a single ring line is preferable for such a dispersed multiprocessor system, from an economical view point, when setting up the same as a ring network. The present invention is preferably applied to a single ring line type network, for example, a dispersed multiprocessor system as mentioned above.
2. Description of the Related Art
Two systems for carrying out a connection management of the ring network accommodating a plurality of nodes are known, for example, a token ring system and a fiber distributed data interface (FDDI) system. The former token ring system by IEEE 802.5 is explained in, for example, "ANSI/IEEE Standard for Local Area Networks: Token Ring Access Method and Physical Layer Specifications, Apr. 29, 1985, 4. Token Ring Protocols" The latter FDDI system by ANSI is explained in, for example, "FDDI TOKEN RING STATION MANAGEMENT (SMT) DRAFT PROPOSED AMERICAN NATIONAL STANDARD X3T9.5, JUL. 25, 1985, 6. Connection Management"
These two known connection management systems will be explained hereinafter in more detail, but first the problems caused by these systems will be discussed.
The known token ring system carries out the connection management by turning a particular control frame around the ring network. Therefore, a detection of a fault, i.e., abnormality, and a recognition of an elimination of the abnormality is delayed by a term required for turning the particular control frame around the ring network. Accordingly, the larger the size of the ring network, the longer becomes the above-mentioned term or delay required for the detection of a fault and recognition of the elimination of the abnormality.
Further, when an abnormality occurs at a monitor node for realizing concentrated management of the ring network, complicated processing must be carried out, such processing includes software processing to enable one of the other normal modes to be used as a new monitor node. Accordingly, it is difficult to apply the token ring system per se to a ring network operated at a high speed of a transmission rate of over 100 Mb/s, due to an overload of the connection management.
Furthermore, each node of the ring network usually holds information regarding the scale of the network. Therefore, if the network is reconstructed due to, for example, the addition of new nodes, this information also must be renewed at the time of the above-mentioned reconstruction. For example, a timer value used for the detection of a fault and the recognition of the elimination of the abnormality, must be renewed to avoid this inconvenience. However it is possible not to renew the timer value by setting same to cope with the maximum expected scale of the network. Such a measure, however, causes a problem in that the above mentioned term for the fault detection and elimination recognition is unnecessary prolonged in a small scale network.
With regard to the known FDDI system, the connection management is carried out between each two adjacent nodes, and thus the system is equivalent to a dispersion control system. In such a FDDI system, it is not necessary to turn control data around the ring network as in the token ring system, and consequently, a high speed management is possible. Also, it is not necessary to form a monitor node as in the token ring system, and accordingly, the control of the FDDI system is simpler than the control of the token ring system.
In the token ring system, however, the system must be formed as a double ring network, and therefore, it is impossible to apply the connection management of the token ring system to the FDDI system as is. If a single ring network is partially formed under the FDDI system, the connection management for the part of the network constituting the single ring network is identical to the connection management of the token ring system, and accordingly, a problem similar to the aforesaid problem of the token ring system is raised.